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Islands are evolution’s laboratories. Think of the Galapagos Islands, where Charles Darwin noted slightly different species on nearby islands, shaping his thoughts on evolutionary divergence and diversification. To Darwin, islands were a microcosm of the processes of change that occurred everywhere: “The principle which determines the general character of the fauna and flora of oceanic islands, namely, that the inhabitants, when not identically the same, yet are plainly related to the inhabitants of that region whence colonists could most readily have been derived,—the colonists having been subsequently modified and better fitted to their new homes,—is of the widest application throughout nature.”1 Alfred Russel Wallace, credited as co-discoverer of Darwinian evolution, shaped his evolutionary theory while travelling through the Malay Archipelago. Wallace’s observation that the neighbouring islands of Bali and Lombok were inhabited by distinctly different faunas spurred the development of the field of biogeography. Jumping forward a century, the publication of “Island Biogeography” by Robert H. Macarthur and Edward O. Wilson marked a key point in the development of a model-based approach to ecology, because they developed a simple mathematical model to explain differences in number of species on islands in terms of the size of the island and its distance from the mainland2.
Islands, though accounting for a tiny proportion of the world’s land area, have had a disproportionately large impact on biological science because they illustrate evolution in action. Why, then, have islands not played a similar role in the understanding of language change and diversity? Linguistic diversity and biodiversity are in many ways very similar. Languages and species both show similar global patterns, with high diversity in the tropics, and fewer, widespread languages toward the poles3. Languages, like species, show patterns of similarity consistent with descent from a common ancestor, so their relationships can be represented by a branching family tree4. These similarities in languages and species are driven by similar, though not identical, process of change and diversification. However, one of the key building blocks of modern biology – that islands represent a microcosm of evolutionary processes, acting as “laboratories” of evolutionary change – has found little traction in linguistics.
Yet there is good reason to believe that islands are also drivers of language diversity. Nearly a fifth of the world’s languages are spoken on islands, even though islands represent less than 1% of the global land area5. Around 10% of languages are endemic to islands, used only (or predominantly) on islands. Why do islands capture so much of the world’s linguistic diversity? To answer this question, we first needed to construct a database of all languages found on over 13,000 inhabited islands. We also needed information on the relationships between languages, particularly because one of the largest language families in the world, Austronesian, was formed by the migration of people across the islands of Oceania. And we needed to take into account the spatial distribution of languages: for example, higher island language diversity could simply be driven by their location in tropical latitudes.
When we analysed this global database, we found that islands play a similar role in generating language diversity as they do for biodiversity. But while number of languages increases with island area, as predicted from island biogeography theory, island language diversity is not predictable from distance from the mainland, perhaps due to special features of human culture and technology. Rather than chance arrivals, people developed both the means and the desire to settle the furthest oceanic islands. The peopling of Oceania, including the remote islands of Hawaii, Aotearoa (New Zealand) and Rapanui (Easter Island), was accomplished by skilled sailors in ocean-going craft, guided by sky, stars and stories. However, one of Darwin’s key observations of species diversity also holds true for languages: “Although in oceanic islands the number of kinds of inhabitants is scanty, the proportion of endemic species (i.e. those found nowhere else in the world) is often extremely large.”1 The number of island endemic languages increases with both island size and distance from mainland5. Island languages also show distinct patterns of evolution, with languages spoken predominantly on islands having significantly fewer phonemes, the basic sound units from which words are made. Islands drive language change and diversification, resulting in islands capturing a greater proportion of the world’s language diversity.
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One way that languages differ from species is in their patterns of endangerment. Biodiversity loss affects all parts of the world, but islands have been particularly severely affected. For example, a fifth of the world’s bird species occur on islands, but 90% of recent bird extinctions have been of island endemic species6. Global linguistic diversity is undergoing a crisis of loss that is as severe as the threat to biodiversity, with more than a third of the world’s languages endangered, and potentially 1500 languages lost by the end of the century7. Many island languages have been lost, particularly due to the disastrous effects of colonisation. For example, the ten languages of the Great Adamanese language family fell silent after colonization devastated the indigenous inhabitants of the Andaman Islands, with the last remaining language spoken by only a few elders. Our analysis shows that island endemic languages do not have significantly higher levels of endangerment than their mainland counterparts. However, because islands hold such a disproportionately large share of the global language diversity, they will play a crucial role in safeguarding linguistic diversity. Islands are not only cradles of linguistic diversity, but also arks carrying languages diversity forward into the future.
For more information see:
L. Bromham, K.J. Yaxley, M. Cardillo (2024) Islands are engines of language diversity. Nature Ecology & Evolution, doi: 10.1038/s41559-024-02488-4. https://www.nature.com/articles/s41559-024-02488-4
References
1) Darwin, C. The origin of species by means of natural selection: or the preservation of favoured races in the struggle for life. First edition edn, (John Murray, 1859).
2) May, R. M. in The Theory of Island Biogeography Revisited (ed Robert E. Ricklefs edited by Jonathan B. Losos) (Princeton University Pres, 2009).
3) Hua, X., Greenhill, S. J., Cardillo, M., Schneemann, H. & Bromham, L. The ecological drivers of variation in global language diversity. Nature Communications 10, 2047, doi:10.1038/s41467-019-09842-2 (2019).
4) Atkinson, Q. D. & Gray, R. D. Curious parallels and curious connections—phylogenetic thinking in biology and historical linguistics. Systematic Biology 54, 513-526 (2005).
5) Bromham, L., Yaxley, K. J. & Cardillo, M. Islands are engines of language diversity. Nature Ecology & Evolution(2024). doi: 10.1038/s41559-024-02488-4.
6) Johnson, T. H. & Stattersfield, A. J. A global review of island endemic birds. Ibis 132, 167-180, doi:https://doi.org/10.1111/j.1474-919X.1990.tb01036.x (1990).
7) Bromham, L. et al. Global predictors of language endangerment and the future of linguistic diversity. Nature Ecology & Evolution https://doi.org/10.1038/s41559-021-01604-y (2021).